Antenna device having wide operation range with a compact size

ABSTRACT

This patent specification describes an antenna device which includes a non-directional antenna having a radiating element and a ground plate, a coaxial line configured to feed an electromagnetic power to the non-directional antenna, a dielectric film arranged on the ground plate, including a dielectric material, a short circuit line arranged on the dielectric film, formed of a conductive pattern and configured to connect an inner conductor of the coaxial line to an outer conductor of the coaxial line and a switch arranged at a portion of the short circuit line to switch a state between a non-shorted state and a shorted state.

FIELD

This patent specification describes an antenna device having wideoperation range with a compact size.

BACKGROUND

Recent rapid development of a radio communication technology realizes avariety of products in communication areas such as mobile phone and aninformation terminal equipped with a variable-directivity antenna. Inthe radio communication areas, it is highly expected to increase atransmission capacity due to a necessity to handle more complicated andlarger data. Many researches and studies have recently been made toattempt an increase of transmission capacity, particularly, bymultiplexing various signals of different dimensions, such as, forexample, time, space, polarized waves and codes.

Multiplexing with space, in particular, can ideally be made with anadaptive array antenna having a plurality of a nondirectional antennasand a circuit for synthesizing vectors of signals from the plurality ofnondirectional antennas. The adaptive array antenna has inherentdisadvantages in a practical usage due to facts that each antenna has arelatively large size and that two adjacent antennas are spaced with arelatively large distance.

An antenna is expected to be as small as possible, especially, in amobile application area. The variable-directivity antenna is generallymade of a pair of an antenna and a power supply circuit and is capableof varying directivity. Such a variable-directivity antenna is believedto be made in a size smaller than the adaptive array antenna and istherefore expected to be a promising candidate for a compact antennathat realizes multiplexing with space. However, only a few studies havebeen announced on a compact variable-directivity antenna device.

FIG. 1 illustrates an oblique perspective view of a knownvariable-directivity antenna device. The variable-directivity antennaincludes an antenna element 101, a reflecting element 102 and areflecting element moving means 103. The reflecting element 102 isarranged in parallel to the antenna element 101. The reflecting elementmoving means 103 includes a rotation drive portion 103 a and aconnection arm 103 b so that the reflecting element 102 moves along acircular-arc around an axial line of the antenna element 101. Thereflecting element 102 is arranged perpendicularly via an insulator (notshown) on the rotation drive portion 103 a.

The rotation drive portion 103 a is attached on a conductor 104, forexample, a car body. Further, the reflecting element 102 is connectedvia the reflecting element moving means 103. A coaxial line 105 connectselectrically the antenna element 101 to a power supply 106. Therefore,the antenna element 101 directs the directivity in a specific directionby adjusting a positional relationship between the antenna element 101and the reflecting element 102. However, a size of the antenna device islarge due to an installation of the reflecting element 102.

FIG. 2 illustrates an oblique perspective view of another knownvariable-directivity antenna device. The variable-directivity antennadevice includes a circular ground plate 111, a single center monopole112 and parasitic elements 113. The parasitic elements 113 are arrangedto surround the single center monopole 112. An impedance load 114 isarranged under a part of the parasitic element 113. A directivity of theantenna device is changed by changing a state of the impedance of theparasitic element 114. However, an interval between the single centermonopole 112 and the parasitic element 113 is limited to be λ/4. As aresult, the antenna size becomes large and a whole size of the antennadevice is more than 2λ.

FIG. 3 illustrates an oblique perspective view of another knownvariable-directivity antenna device 115. The variable-directivityantenna 115 includes a radiating element A0 and variable reactanceelements A1 to A6 and a circular ground plate 116. A radio signal is fedto the radiating element A0. The variable reactance elements A1 to A6are radially arranged to surround the radiating element A0. However, aninterval d between the radiating element A0 and the variable reactanceelements A1 to A6 is to be λ/4. As a result, a size of the antennadevice 115 becomes large and is more than λ. As described, the proposedvariable-directivity antenna devices are larger than the non-directionalantenna device.

FIG. 4A illustrates a cross-sectional view of another knownvariable-directivity antenna device 120. FIG. 4B illustrates a top viewof a part of the known antenna device 120 of FIG. 4A. The antenna device120 is a disk-corn-shaped antenna having a radiating element 121 and aground plate 123. The antenna device 120 is a non-directional antenna towhich an electromagnetic power is fed by a coaxial line 124.

FIG. 5 illustrates a return loss characteristic of thevariable-directivity antenna device 120 of FIG. 4A. Similar values ofthe return loss are obtained in a wide range independent of theexistence of the short circuit. However, the return loss is increased ina range below a frequency of 10 GHz. An inductance due to the shortcircuit is increasing perpendicular to the increase of the frequency.However, the inductance in the range of the frequency of 10 GHz is notlarge enough to affect an inductance of the antenna device.

FIG. 6 illustrates a cross-sectional view of another knownvariable-directivity antenna device 130. The antenna device 130 includesa coaxial line 134, an inner conductor 134 a, an outer conductor 134 b,short-circuit 131, switches 133 and a capacitor 135 on a ground plate137. The short-circuit line 131 shorts the inner conductor 134 a and theouter conductor 134 b of the coaxial line 134. The switch 133 switches astate between a shorted state and a non-shorted state. In the antennadevice 130, wirings are eliminated using flip chip methodology in anassembly process so as to improve accuracy with less difference amongantenna devices.

FIG. 7 illustrates a cross-sectional view of the variable-directivityantenna device 130 of FIG. 6 with wirings to make a short-circuit in ashorted state. FIG. 8 illustrates a cross-sectional view of thevariable-directivity antenna device 130 of FIG. 6 with no wiring.

There is a need for a variable-directivity antenna having a wideoperating range with a similar size to a non-directional antenna device.

SUMMARY

This patent specification describes a novel antenna device whichincludes a non-directional antenna having a radiating element and aground plate, a coaxial line configured to feed an electromagnetic powerto the non-directional antenna, a dielectric film arranged on the groundplate, including a dielectric material, a short circuit line arranged onthe dielectric film, formed of a conductive pattern and configured toconnect an inner conductor to an outer conductor of the coaxial line anda switch arranged at a portion of the short circuit line to switch astate between a non-shorted state and a shorted state.

This patent specification further describes a novel antenna device whichincludes a non-directional antenna having a radiating element and aground plate, a coaxial line configured to feed an electromagnetic powerto the non-directional antenna, a dielectric film arranged on the groundplate and formed of dielectric material, a short circuit line arrangedon the dielectric film, formed of a conductive pattern and configured toconnect an inner conductor to an outer conductor of the coaxial line anda capacitor configured to connect an outer portion of the short circuitto the ground plate at a radio frequency at a position outside an outerconductor of the coaxial line from the center of the coaxial line overthe ground plate.

Further, this patent specification describes a novel antenna devicewhich includes a non-directional antenna having a radiating element anda ground plate, a coaxial line configured to feed an electromagneticpower to the non-directional antenna, a short circuit line arranged on adielectric film, formed of a conductive pattern and having a lengthsubstantially longer than an interval between an inner conductor and anouter conductor of the coaxial line and a switch arranged at a portionof the short circuit to switch a state between a non-shorted state and ashorted state.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosure and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 illustrates a known variable-directivity antenna device;

FIG. 2 illustrates another known variable-directivity antenna device;

FIG. 3 illustrates another known variable-directivity antenna device;

FIG. 4A illustrates an oblique perspective view of another knownvariable-directivity antenna device;

FIG. 4B illustrates a top view of a part of the antenna device of FIG.4A;

FIG. 5 illustrates a return loss characteristic of thevariable-directivity antenna device of FIG. 4A;

FIG. 6 illustrates a cross-sectional view of another knownvariable-directivity antenna device;

FIG. 7 illustrates a cross-sectional view of the variable-directivityantenna device of FIG. 6 having active short-circuit with wirings;

FIG. 8 illustrates a cross-sectional view of the variable-directivityantenna device of FIG. 6 with no wiring;

FIGS. 9A and 9B illustrate a relevant part of an antenna deviceaccording to a first exemplary embodiment;

FIG. 9C illustrates an example of an equivalent circuit of a switch ofFIG. 9A;

FIG. 9D illustrates a characteristics of the antenna device to explainthe directivity of the variable-directional antenna device of FIG. 9A;

FIGS. 10A and 10B illustrate a relevant part of an antenna deviceaccording to a second exemplary embodiment;

FIGS. 11A and 11B illustrate a relevant part of an antenna deviceaccording to a third exemplary embodiment;

FIGS. 12A and 12B illustrate a relevant part of an antenna deviceaccording to a fourth exemplary embodiment;

FIGS. 13A and 13B illustrate a relevant part of an antenna deviceaccording to a fifth exemplary embodiment;

FIG. 13C illustrates a graph of a return loss of the antenna device of13A;

FIGS. 14A and 14B illustrate a relevant part of an antenna deviceaccording to a sixth exemplary embodiment;

FIGS. 15A and 15B illustrate a relevant part of an antenna deviceaccording to a seventh exemplary embodiment; and

FIGS. 16A and 16B illustrate a relevant part of an antenna deviceaccording to an eighth exemplary embodiment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In describing preferred embodiments illustrated in the drawings,specific terminology is employed for the sake of clarity. However, thedisclosure of this patent specification is not intended to be limited tothe specific terminology so selected and it is to be understood thateach specific element includes all technical equivalents that operate ina similar manner. Referring now to the drawings, wherein like referencenumerals designate identical or corresponding parts throughout theseveral views, particularly to FIGS. 9A, 9B, 13A, 13B, 14A and 14B,antenna devices according to exemplary embodiments are described.

FIGS. 9A and 9B illustrate a relevant part of an antenna device 100according to a first exemplary embodiment. FIG. 9A illustrates anoblique perspective view of the antenna device 100 according to thefirst exemplary embodiment. FIG. 9B illustrates a cross-sectional viewof the antenna device 100 of FIG. 9A. The antenna device 100 is adisk-corn-shaped antenna having a radiating element 3 and a ground plate5. The antenna device 100 is a variable-directional antenna to which anelectromagnetic power is fed by a coaxial line 1.

The antenna device 100 further includes a dielectric film 15,short-circuit lines 11, switches 9 and capacitors 13. The dielectricfilm 15 includes a dielectric material and is arranged on the groundplate 5. The short-circuit line 11 shorts an inner conductor 1 a and anouter conductor 1 b of the coaxial line 1. Each switch 9 is arranged ata portion of the short-circuit line 11 and switches a state between ashorted state and a non-shorted state. The capacitor 13 connects theshort-circuit line 11 to the ground plate 5 at a radio frequency.

Namely, a connection portion between the radiating element 3 and thecoaxial line 1 comprises bias lines 7, the switches 9, the short-circuitlines 11 and the dielectric film 15 on the ground plate 5. An electrode13 a of the capacitor 13 is formed on the dielectric film 15. Theswitches 9 can selectively be turned ON or OFF with the short-circuitlines 11 in four directions.

The capacitor 13 further includes other electrode 17 in addition to theelectrode 13 a and the dielectric film 15. The electrodes 13 a and 17are formed of metal pattern on the dielectric film 15. The electrodes 13a is made in a process in which the short circuit line 11 is made. Anoutline pattern of the capacitor 13 includes a circular arc portion 13 bwhich is circular about a center of the coaxial line 1 and a linearshape portion 13 c which is expanding in a radiating direction. Thecapacitor 13 is closely located to the coaxial line 1, but is configuredto have a space between each capacitor element so as not to prevent acurrent flow on the ground plate 5, which contributes radiation.

In this exemplary embodiment, a PIN (p-type, intrinsic, n-type) diode isused as the switch 9. The switches 9 can be controlled to turn ON or OFFwith the short-circuit lines 11 from an outside of the antenna device100 through bias lines 7. When all of the switches are turned OFF, aradiation pattern of the antenna device 100 remains non-directionalbecause there is no disturbance to the electric field of the coaxialline 1.

When one of the switches is turned ON, the radiation pattern of theantenna device 100 obtains a directivity because the electric field ofthe coaxial line 1 is disturbed. The directivity of the antenna 100 canbe switched by switching the switches 9.

FIG. 9C illustrates an example of an equivalent circuit of the switch 9of FIG. 9A and 9B. In FIG. 9C, symbols A, B, and E show terminals, asymbol D shows the PIN diode, a symbol C shows the capacitor 13, asymbol L shows inductance and a symbol R shows a resistance. Theterminal A is connected to a signal line of the coaxial line 1. Theterminal B is connected to a ground line of the coaxial line 1. Theterminal E is connected to the bias line 7 formed on the dielectric film15. The PIN diode D is connected to the ground by the capacitor C at aradio frequency. The PIN diode D performs a switching operation byutilizing a large change of a resistance value of the PIN diode D inaccordance with a change of a DC bias value applied to the terminal E.

FIG. 9D illustrates characteristics of the antenna device 100 to explainthe directivity of the variable-directional antenna device 100 accordingto the first exemplary embodiment. In FIG. 9D, antenna gaincharacteristics at an angle of 45 degree from the ground plate 5 areillustrated for a 360-degree field around the radiator when a base angle(0 degree) is determined at a direction of a switch 9 which is turnedON.

In FIG. 9D, a solid line shows an antenna gain characteristic when oneswitch 9 located on a line of the base angle (0 degree) is turned ON. Adotted line shows the antenna gain characteristic when all of theswitches 9 are turned OFF. Referring to FIG. 9D, the antenna gain isfound to be a constant value at any angle. Further, a radiation patternof the antenna device 100 is non-directional when all of the switches 9are turned OFF.

The radiation pattern of the antenna device 100 is changed by turning apredetermined switch 9 ON. A radiation intensity of the antenna device100 becomes strong when the switch 9 at an opposite side is turned ON.Thus, a radiation direction of the antenna device 100 having a similarsize to a common non-directional antenna can be changed.

Because the variable-directional antenna 100 according to the firstexemplary embodiment includes the capacitor 13 formed with thedielectric film 15, the variable-directional antenna 100 having asimilar size to the common non-directional antenna may be possible tooperate in a similar frequency range to the common non-directionalantenna. Moreover, the characteristics of the antenna is improved byeliminating wiring to make a contact with the coaxial line 1. Further,an assembly process becomes simple so that a cost reduction can beachieved.

FIGS. 10A and 10B illustrate a relevant part of an antenna device 200according to a second exemplary embodiment. FIG. 10A illustrates anoblique perspective view of the antenna device 200 according to thesecond exemplary embodiment. FIG. 10B illustrates a cross-sectional viewof the antenna device 200 of FIG. 10A. The antenna device 200 is adisk-corn-shaped antenna having a radiating element 203 and a groundplate 205. The antenna device 200 is a variable-directional antenna towhich an electromagnetic power is fed by a coaxial line 201.

The antenna device 200 further includes a dielectric film 215,short-circuit lines 211, switches 209 and capacitors 213. The dielectricfilm 215 includes a dielectric material and is arranged on the groundplate 205. The short-circuit line 211 shorts an inner conductor 201 aand an outer conductor 201 b of the coaxial line 201. The switch 209 isarranged at a portion of the short-circuit line 211 and switches a statebetween a shorted state and a non-shorted state. The capacitor 213connects the short-circuit line 211 to the ground plate 205 at a radiofrequency.

Namely, a connection portion between the radiating element 203 and thecoaxial line 201 comprises bias lines 207, the switches 209, theshort-circuit lines 211 and the dielectric film 215 on the ground plate205. An electrode 213 a of the capacitor 213 is formed on the dielectricfilm 215. The switches 209 can selectively be turned ON or OFF with theshort-circuit lines in four directions.

In this second exemplary embodiment, the capacitor 213 is formed withthe electrode 213 a, the dielectric film 215 and a part of the groundplate 205. The electrodes 213 a is formed of metal pattern on thedielectric film 215. The electrodes 213 a is made in a process in whichthe short circuit line 211 is made. The other electrode is formed with apart of the ground plate 205. An outline pattern of the capacitor 213includes a circular arc portion 213 b which is circular about a centerof the coaxial line 201 and a linear shape portion 213 c which isexpanding in a radiating direction. The capacitor 213 is closely locatedto the coaxial line 201, but is configured to have a space between eachcapacitor element so as not to prevent a current flow on the groundplate 205, which contributes radiation.

In this exemplary embodiment, a PIN diode is used as the switch 209. Theswitches 209 can be controlled to turn ON or OFF with the short-circuitlines 211 from an outside of the antenna device 200 through the biaslines 207. When all of the switches are turned OFF, a radiation patternof the antenna device 200 remains non-directional because there is nodisturbance to the electric field of the coaxial line 201.

When one of the switches is turned ON, a radiation pattern of theantenna device 200 has a directivity because the electric field of thecoaxial line 201 is disturbed. The directivity of the antenna 200 can beswitched by switching the switches 209. Because the variable-directionalantenna 200 according to the second exemplary embodiment includes thecapacitor 213 formed with the dielectric film 215, thevariable-directional antenna 200 having a similar size to the commonnon-directional antenna may be possible to operate in a similarfrequency range to the common non-directional antenna.

FIGS. 11A and 11B illustrate a relevant part of an antenna device 300according to a third exemplary embodiment. FIG. 11A illustrates anoblique perspective view of the antenna device 300 according to thethird exemplary embodiment. FIG. 11B illustrates a cross-sectional viewof the antenna device 300 of FIG. 11A. The antenna device 300 is adisk-corn-shaped antenna having a radiating element 303 and a groundplate 305. The antenna device 300 is a variable-directional antenna towhich an electromagnetic power is fed by a coaxial line 301.

The antenna device 300 further includes a dielectric film 315,short-circuit lines 311, switches 309 and capacitors 313. The dielectricfilm 315 includes a dielectric material and is arranged on the groundplate 305. The short-circuit line 311 shorts an inner conductor 301 aand an outer conductor 301 b of the coaxial line 301. The switch 309 isarranged at a portion of the short-circuit line 311 and switches a statebetween a shorted state and a non-shorted state. The capacitor 313connects the short-circuit line 311 to the ground plate 305 at a radiofrequency.

Namely, a connection portion between the radiating element 303 and thecoaxial line 301 comprises bias lines 307, the switches 309, theshort-circuit lines 311 and the dielectric film 315 on a support plate321. An electrode 313 a of the capacitor 313 and a ground plate 323 areformed on the dielectric film 315. The ground plate 323 is formed byextending the other electrode 323 a. The switches 309 can selectively beturned ON or OFF with the short-circuit lines in four directions.

The capacitor 313 further includes other electrode 323 a in addition tothe electrode 313 a and the dielectric film 315. The electrodes 313 aand 323 a are formed of metal pattern on the dielectric film 315. Theelectrodes 313 a is made in a process in which the short circuit line311 is made. An outline pattern of the capacitor 313 includes a circulararc portion 313 b which is circular about a center of the coaxial line301 and a linear shape portion 313 c which is expanding in a radiatingdirection. The capacitor 313 is closely located to the coaxial line 301,but is configured to have a space between each capacitor element so asnot to prevent a current flow on the ground plate 305, which contributesradiation. A circumferential length of the circular arc portion 313 b islonger than the circumferential length of the circular arc portion ofthe first and second exemplary embodiments.

In this exemplary embodiment, a PIN diode is used as the switch 309. Theswitches 309 can be controlled to turn ON or OFF with the short-circuitlines 311 from an outside of the antenna device 300 through the biaslines 307. When all of the switches are turned OFF, a radiation patternof the antenna device 300 remains non-directional because there is nodisturbance to the electric field of the coaxial line 301.

When one of the switches is turned ON, the radiation pattern of theantenna device 300 possess a directivity because the electric field ofthe coaxial line 301 is disturbed. The directivity of the antenna 300can be switched by switching the switches 309. Because thevariable-directional antenna 300 according to the third exemplaryembodiment includes the capacitor 313 formed with the dielectric film315, the variable-directional antenna 300 having a similar size to thecommon non-directional antenna may be possible to operate in a similarfrequency range to the common non-directional antenna.

FIGS. 12A and 12B illustrate a relevant part of an antenna device 400according to a fourth exemplary embodiment. FIG. 12A illustrates anoblique perspective view of the antenna device 400 according to thefourth exemplary embodiment. FIG. 12B illustrates a cross-sectional viewof the antenna device 400 of FIG. 12A. The antenna device 400 is adisk-corn-shaped antenna having a radiating element 403 and a groundplate 405. The antenna device 400 is a variable-directional antenna towhich an electromagnetic power is fed by a coaxial line 401.

The antenna device 400 further includes a dielectric film 415,short-circuit lines 411, switches 409 and capacitors 413. The dielectricfilm 415 includes a dielectric material and is arranged on the groundplate 405. The short-circuit line 411 shorts an inner conductor 401 aand an outer conductor 401 b of the coaxial line 401. The switch 409 isarranged at a portion of the short-circuit line 411 and switches a statebetween a shorted state and a non-shorted state. The capacitor 413connects the short-circuit line 411 to the ground plate 405 at a radiofrequency. Namely, a connection portion between the radiating element403 and the coaxial line 401 comprises bias lines 407, the switches 409,the short-circuit lines 411 and the dielectric film 415 on the groundplate 405.

The capacitor 413 includes the electrode 413 a, other electrode 417 anda thin dielectric film 425. The electrodes 413 a is formed of metalpattern on a lower side of the dielectric film 415 and is made in aprocess in which the short circuit line 411 is made. The thin dielectricfilm 425 is thinner than the dielectric film 415 so that larger capacityvalue is obtained with a similar capacitor area using the dielectricfilm 415. The thin dielectric film 425 is formed on the grand plate 405.

An outline pattern of the capacitor 413 includes a circular arc portion413 b about a center of the coaxial line 401 and a linear shape portion413 c which is expanding in a radiating direction. The capacitor 413 isclosely located to the coaxial line 401, but is configured to have aspace between each capacitor element so as not to prevent a current flowon the ground plate 405, which contributes radiation.

In this exemplary embodiment, a PIN diode is used as the switch 409. Theswitches 409 can be controlled to turn ON or OFF with the short-circuitlines 411 from an outside of the antenna device 400 through the biaslines 407. When all of the switches are turned OFF, a radiation patternof the antenna device 400 remains non-directional because there is nodisturbance to the electric field of the coaxial line 401.

When one of the switches is turned ON, the radiation pattern of theantenna device 400 attains a directivity because the electric field ofthe coaxial line 401 is disturbed. The directivity of the antenna 400can be switched by switching the switches 409. Because thevariable-directional antenna 400 according to the fourth exemplaryembodiment includes the capacitor 413 formed with the dielectric film415, the variable-directional antenna 400 having a similar size to thecommon non-directional antenna may be possible to operate in a similarfrequency range to the common non-directional antenna.

FIGS. 13A and 13B illustrate a relevant part of an antenna device 500according to a fifth exemplary embodiment. FIG. 13A illustrates anoblique perspective view of the antenna device 500 according to thefifth exemplary embodiment. FIG. 13B illustrates a cross-sectional viewof the antenna device 500 of FIG. 13A. The antenna device 500 is adisk-corn-shaped antenna having a radiating element 503 and a groundplate 505. The antenna device 500 is a variable-directional antenna towhich an electromagnetic power is fed by a coaxial line 501.

On the ground plate 505, bias lines 507, switches 509, short-circuitlines 511 and a dielectric film 515 are arranged. The dielectric film515 includes a dielectric material and is attached on the ground plate505. The short-circuit line 511 shorts an inner conductor 501 a and anouter conductor 501 b of the coaxial line 501. The switch 509 isarranged at a portion of the short-circuit line 511 and switches a statebetween a shorted state and a non-shorted state. An electrode 513 a of acapacitor 513 is formed on the dielectric film 515. The switches 509 canselectively be turned ON or OFF with the short-circuit lines 511 in fourdirections at a connection portion between the radiating element 503 andthe coaxial line 501. The capacitor 513 is formed with a metal patternon the dielectric film 515, an electrode, the dielectric film 515 andthe ground plate 505.

An outline pattern of the capacitor 513 includes a circular arc portion513 b which is circular about a center of the coaxial line 501 and alinear shape portion 513 c which is expanding in a radiating direction.The capacitor 513 is closely located to the coaxial line 501, but isconfigured to have a space between each capacitor element so as not toprevent a current flow on the ground plate 505, which contributesradiation.

In terms of a radio frequency, a grounded point of the short-circuitline 511 at a side of an outer conductor 510 of the coaxial line 501 islocated at a connection point to the capacitor 513. Namely, the groundedpoint of the short-circuit line 511 is located at a position which isoutside of outer conductor 510 of the coaxial line 501 from the centerof the coaxial line 501 and over the ground plate 505. In theconfiguration of the fifth exemplary embodiment, the short-circuit lines511 can be made substantially longer. An inductance caused by theshort-circuit lines 511 can be made larger.

As for the switch 509, various switching devices which can be turned ONand OFF electrically are used, for example, a diode switch or a MEMS(Micro Electro Mechanical Systems) switch. A PIN diode is used as theswitch 509 in this exemplary embodiment. The switches 509 can becontrolled to turn ON or OFF with the short-circuit lines 511 from anoutside of the antenna device 500 through the bias lines 507. When allof the switches are turned OFF, a radiation pattern of the antennadevice 500 remains non-directional because there is no disturbance onthe electric field of the coaxial line 501.

When one of the switches 509 is turned ON, the radiation pattern of theantenna device 500 has a directivity because the electric field of thecoaxial line 501 is disturbed. The directivity of the antenna 500 can beswitched by switching the switches 509.

FIG. 13C illustrates a graph of a return loss of the antenna device 500according to the fifth exemplary embodiment. A solid line shows acharacteristic of the antenna device 500. A dotted line shows acharacteristic of a conventional antenna device in which theshort-circuit line 511 is connected with a straight line. Referring toFIG. 13C, the return loss of the antenna device according to the fifthexemplary embodiment has a lower return loss in a range below 10 GHz andis found to be improved. It is possible to improve the radiationcharacteristic in the lower frequency range because the short-circuitlines 511 are made substantially longer than the conventional antennadevice and the inductance caused by the short-circuit lines 511 is madesubstantially larger.

The characteristic of the return loss of FIG. 13C is slightly differentfrom the return loss FIG. 5. This is due to a difference of theconfiguration of the antenna devices. More specifically, thecharacteristic of the return loss of FIG. 13C is measured using theantenna device 500 having the dielectric film but the characteristic ofthe return loss of FIG. 5 is measured using the antenna device with nodielectric film.

FIG. 14A and 14B illustrate a relevant part of an antenna device 600according to a sixth exemplary embodiment. FIG. 14A illustrates anoblique perspective view of the antenna device 600 according to thesixth exemplary embodiment. The antenna device 600 is a disk-corn-shapedantenna having a radiating element 603 and a ground plate 605. FIG. 14Billustrates a top view of the ground plate 605 of the antenna device 600of FIG. 14A. The antenna device 600 is a variable-directional antenna towhich an electromagnetic power is fed by a coaxial line 601.

As shown in FIG. 14B, each short-circuit line 621 includes ameander-shaped line in each of four directions to connect to each switch609 so that a length of the short-circuit line 621 is extendedsubstantially. In this exemplary embodiment, a center of the coaxialline 601, a connection point of the short-circuit line 621 and a innerconductor 601 a and a connection point of the short-circuit line 621 andan outer line 610 are arranged on a straight line.

An electric field direction of TEM mode (Transverse Electromagneticmode) matches with a shorting direction so that a length of theshort-circuit line 521 is made substantially longer without disturbingother electric field in the coaxial line 601 than the electric field inthe shorting direction. Therefore, it is possible to improve theradiational characteristic in the lower frequency range. As for theswitch 609, the switching devices which can be turned ON and OFFelectrically are used, for example, a diode switch or a MEMS switchsimilar to the fifth exemplary embodiment.

FIGS. 15A and 15B illustrate a relevant part of an antenna device 700according to a seventh exemplary embodiment. FIG. 15A illustrates anoblique perspective view of the antenna device 700 according to theseventh exemplary embodiment. FIG. 15B illustrates a cross-sectionalview of a ground plate 705 of the antenna device 700 of FIG. 15A. Theantenna device 700 is a disk-corn-shaped antenna having a radiatingelement 703 and a ground plate 705. The antenna device 700 is avariable-directional antenna to which an electromagnetic power is fed bya coaxial line 701.

The antenna device 700 has both features of the antenna devices 500 and600 according to the fifth and sixth exemplary embodiments,respectively. Namely, bias lines 707, switches 709, short-circuit lines711 and a dielectric film 715 are arranged on the ground plate 705. Thedielectric film 715 includes a dielectric material and is attached onthe ground plate 705. Moreover, each short-circuit line 721 has ameander-shaped line in each of four directions to connect to each switch709 so that a length of the short-circuit line 721 is extendedsubstantially.

Two expanding effects of short-circuit line, which is substantiallyextending the length of the short-circuit line, will be obtainedaccording to the seventh exemplary embodiment. Namely, one expandingeffect of short-circuit line is achieved by configuring the groundedpoint of the short-circuit line 721 to be located at a point which is onan outer side of an outer conductor 710 of the coaxial line 701 from thecenter of the coaxial line 701 and over the ground plate 705. Anotherexpanding effect of short-circuit line is achieved by the formation ofthe short-circuit line with a meander-shaped line. An inductance of theshort-circuit line 721 is increased so that a radiation characteristiccan be improved in the lower frequency range.

FIGS. 16A and 16B illustrate a relevant part of an antenna device 800according to an eighth exemplary embodiment. FIG. 16A illustrates anoblique perspective view of the antenna device 800 according to theeighth exemplary embodiment. FIG. 16B illustrates a cross-sectional viewof a ground plate 805 of the antenna device 800 of FIG. 16A. The antennadevice 800 is a disk-corn-shaped antenna having a radiating element 803and a ground plate 805. The antenna device 800 is a variable-directionalantenna to which an electromagnetic power is fed by a coaxial line 801.

The antenna device 800 includes a high magnetic permeability material,for example ferrite, which is the sole difference from the antennadevice 500 of the fifth exemplary embodiment. The high magneticpermeability material is arranged at a position of the coaxial line 801close to short-circuit lines 821. A permeability value of the highmagnetic permeability material is determined to be grater than “1”.

A inductance of the antenna device 800 is increased by the installationof the high magnetic permeability material having a permeability morethan “1” at a position close to short-circuit lines 821 and by theexpanding effect of the short-circuit line formed to have ameander-shaped line. As a result, an inductance of the short-circuitline 821 is increased so that a radiation characteristic in the lowerfrequency range is improved. Japanese laid open patent application JPOPNo. H10-154911 states that an impedance value depends on the magneticpermeability of the coaxial line.

In the antenna devices of the sixth, seventh and eighth exemplaryembodiments, PIN diodes are used as switching devices. When all of theswitches are turned OFF, a radiation pattern of the antenna device (600,700, 800) remains non-directional. When one of the switches is turnedON, the radiation pattern of the antenna device (600, 700, 800) possessa directivity. Thus, the directivity of the antenna 600, 700 and 800 canbe switched by switching the switch 609, 709 and 809, respectively.

Numerous additional modifications and variations are possible in lightof the above teachings. It is therefore to be understood that within thescope of the appended claims, the disclosure of this patentspecification may be practiced otherwise than as specifically describedherein. For example, elements and/or features of different illustrativeembodiments and examples may be combined with each other and/orsubstituted for each other within the scope of this disclosure andappended claims.

This patent specification is based on Japanese patent applications, No.2005-204642 filed on Jul. 13, 2005 and No. 2005-209267 filed on Jul. 19,2005 in the Japan Patent Office, the entire contents of which areincorporated by reference herein.

1. An antenna device, comprising: a non-directional antenna having aradiating element and a ground plate; a coaxial line configured to feedan electromagnetic power to the non-directional antenna, said coaxialline including an inner conductor and an outer conductor; a dielectricfilm arranged on the ground plate, including a dielectric material; ashort circuit line arranged on the dielectric film, formed of aconductive pattern and configured to connect the inner conductor of theaxial line to the outer conductor of the coaxial line; and a switcharranged at a portion of the short circuit line to switch a statebetween a non-shorted state and a shorted state.
 2. The antenna deviceof claim 1, further comprising: a capacitor configured to connect theshort circuit line to the ground plate at a radio frequency andincluding a dielectric layer formed of the dielectric film.
 3. Theantenna device of claim 2, wherein one electrode of the capacitor isformed on a side of the dielectric film with a conductive pattern madein a process in which the short circuit line is made and the otherelectrode of the capacitor is formed at an opposite side of thedielectric film of the capacitor.
 4. The antenna device of claim 3,wherein the other electrode of the capacitor is a part of the groundplate.
 5. The antenna device of claim 3, wherein the ground plate isformed by extending the other electrode of the capacitor.
 6. The antennadevice of claim 1, further comprising: a thin dielectric film thinnerthan the dielectric film formed on the ground plate; and a capacitorincluding a dielectric layer formed of the thin dielectric film andconfigured to connect the short circuit line to the ground plate at aradio frequency, wherein one electrode of the capacitor is formed on aside of the dielectric film with a conductive pattern made in a processin which the short circuit line is made and the other electrode of thecapacitor is formed at opposite side of the thin dielectric film of thecapacitor.
 7. An antenna device, comprising: a non-directional antennahaving a radiating element and a ground plate; a coaxial line configuredto feed an electromagnetic power to the non-directional antenna, saidcoaxial line including an inner conductor and an outer conductor; adielectric film arranged on the ground plate and formed of dielectricmaterial; a short circuit line arranged on the dielectric film, formedof a conductive pattern and configured to connect the inner conductor ofthe coaxial line to the outer conductor of the coaxial line; and acapacitor configured to connect an outer portion of the short circuit tothe ground plate at a radio frequency at a position outside an outerconductor of the coaxial line from the center of the coaxial line overthe ground plate.
 8. An antenna device, comprising: a non-directionalantenna having a radiating element and a ground plate; a coaxial lineconfigured to feed an electromagnetic power to the non-directionalantenna, said coaxial line including an inner conductor and an outerconductor; a short circuit line arranged on a dielectric film, formed ofa conductive pattern and having a length substantially longer than aninterval between the inner conductor of the coaxial line and the outerconductor of the coaxial line; and a switch arranged at a portion of theshort circuit line to switch a state between a non-shorted state and ashorted state.
 9. The antenna device of claim 7, wherein a center axisof the coaxial line, a connection point of the short circuit and theinner conductor, and a connection point of the short circuit line andthe outer conductor are arranged on a straight line.
 10. The antennadevice of claim 7, wherein the short circuit line is formed to have ameander-shaped line.
 11. The antenna device of claim 8, wherein thecoaxial line includes a magnetic permeability material which has apermeability value greater than “1” at a position close to theshort-circuit line in the coaxial line.